FIG. 1 shows an example of a supercharged internal combustion engine 1 which has intake and exhaust passages 3 and 5 connected to intake and exhaust manifolds 2 and 4 of the engine 1, respectively. The exhaust passage 5 is provided with a turbine 7 driven by an exhaust gas 6, and the intake passage 3 is provided with a compressor 8 which produces compressed air 9 with the turbine 7. The turbine 7 and the compressor 8 make up a supercharger 10 as a turbocharger so as to supply the air 9 compressed by the compressor 8 of the supercharger 10 to the intake passage 3 in which an intercooler 12 is incorporated downstream of the compressor 8 and before the intake manifold 2. In FIG. 1, reference numerals 11, 13 and 14 denote an air cleaner, cylinders of the engine 1 and a fuel injector, respectively.
Disposed between the intake and exhaust passages 3 and 5 is an EGR means 15. The EGR means 15 of FIG. 1 interconnects the intake and exhaust manifolds 2 and 4 through an EGR piping (EGR passage) 16 provided with an EGR cooler 17 and an EGR valve 19 opened/closed by an actuator 18.
An accelerator pedal (not shown) of a driver seat is provided with an accelerator sensor (load sensor) 20 which detects an accelerator opening degree as a load of the engine 1. The engine 1 is equipped with a rotation sensor 21 which detects a rotation number thereof. Accelerator opening degree and rotation number signals 20a and 21a of the sensors 20 and 21, respectively, are input to a controller 22 which constitutes an engine control computer (ECU: Electronic Control Unit).
On the other hand, the controller 22 outputs an opening degree command signal 18a which gives a command for an opening degree to the actuator 18 of the EGR valve 19 as well as a fuel injection signal 14a which gives commands for injection timing and amount of fuel to the fuel injector 14 for injecting fuel into the cylinders 13.
During an operation of the engine 1, the controller 22 controls the EGR valve 19 on the basis of the accelerator opening degree and rotation number signals 20a and 21a to maintain the opening degree of the EGR valve 19 at a position depending on an operating state of the engine 1, thereby recirculating the EGR gas to the intake passage 3 for reduction of NOx in the exhaust gas.
The internal combustion engine is equipped with an intake manifold temperature sensor (not shown) adjacent to an inlet of the intake manifold 2. An intake manifold temperature signal from the intake manifold temperature sensor is input to the controller 22 and is utilized for various controls.
Some prior art literatures describe those including two intake-air temperature sensors which detect intake-air temperatures upstream and downstream of a supercharger and utilizing the two intake-air temperature sensors under the condition of, for example, a boost pressure to detect a failure of the intake-air temperature sensors (see, for example, Patent Literature 1).